This invention relates generally to gasket sealed valves of ball type; and more particularly concerns pressurization of such gaskets.
There is need for provision of a valve for pipe line use wherein the working parts of the valve can be maintained in a closed and sealed valve stopper chamber, out of communication with the flowable material in the pipe line, when the valve stopper is in its valve open and valve closed positions.
This feature is very important for standby or safety shut-off valves where the valve stopper normally remains in one position for long periods of time. Often, the position of the valve stopper of such valves is changed only when there is some unusual pipe line emergency.
Pipe lines often carry flowable materials containing varying amounts of very small, solid particles. The solid particles have a tendency to "settle out" in the quiet flow zones of valve stopper chambers that are not completely closed and sealed. Over time, an accumulation of solid particles in the valve stopper chamber may seriously interfere with the working parts of the valve.
There is also a need to provide means for equalizing the thrusting force applied to each sealing gasket during and after the sealing operation has taken place, in order that variations in fluid pressure acting against the valve stopper will not change the effectiveness of the sealing gaskets.
Assume, for instance, that after the valve stopper has been moved to the "valve closed" position, there is an increase in fluid pressure on one side of the valve stopper and little or no fluid pressure on the other side of the stopper. Because of trunnion bearing clearances, the stopper tends to move towards the low pressure side, and would normally tend to decrease the thrusting force being exerted against the gasket on the high pressure side. There is need for means operable to assure that the thrusting force exerted against each gasket remains substantially the same.